Ammonium Platinocyanide, (NH₄)₂Pt(CN)₄

Ammonium Platinocyanide, (NH₄)₂Pt(CN)₄.2H₂O, is obtained when freshly prepared platinous cyanide is dissolved in ammonium cyanide solution. This method, however, does not give a perfectly pure product.

It may be prepared in a pure state by decomposing the barium derivative with ammonium sulphate solution. On concentrating the solution the salt crystallises out in citron-yellow prismatic needles which exhibit interesting trichroism, appearing greenish yellow, lavender-blue or rose colour according to position. Exposed over calcium chloride or sulphuric acid it loses one molecule of water, becoming white. At 100° to 150° C. it loses the whole of its water. The anhydrous salt may also be obtained by conducting ammonia gas over hydrogen platinocyanide at 100° C. At 300° C. it decomposes, yielding platinous cyanide. The monohydrated salt absorbs a second molecule of water on exposure to moist air.